The immediate aim of this protocol is to obtain hematopoietic stem cells from many human donors for examination of the biological properties of those cells. The study is also designed to determine if the donor-specific factors can influence the properties of their hematopoietic stem cells. Each volunteer will undergo stem cell mobilization after administration of granulocyte-colony stimulating factor (G-CSF) for five consecutive days followed by a large volume apheresis on the 5th day after G-CSF injection. The harvested product will be purified for the primitive hematopoietic progenitor cells and viably preserved in multiple aliquots. The cells will then be studied in-depth for a better understanding of their biological properties, growth and differentiation. Donor-specific information will be correlated with these research studies to identify factors that may assist with the understanding of adult stem cell biology.